Exoplanet Populations and their Dependence on Host Star Properties

Exoplanets around different types of stars provide a window into the diverse environments in which planets form. This chapter describes the observed relations between exoplanet populations and stellar properties and how they connect to planet formation in protoplanetary disks. Giant planets occur more frequently around more metal-rich and more massive stars. These findings support the core accretion theory of planet formation, in which the cores of giant planets form more rapidly in more solid-rich and more gas-rich protoplanetary disks. Smaller planets, those with sizes roughly between Earth and Neptune, exhibit different scaling relations with stellar properties. These planets orbit stars with a range of metallicities and occur more frequently around lower mass stars, indicating that planet formation takes place in a wide range of environments. Within M dwarfs, both radial velocity and transit surveys show that planets are smaller and located closer to the star when the stellar mass is lower. Additions to the core accretion model, in particular pebble accretion, have shown success in explaining the enhanced planet formation efficiency around low mass stars.